Santorum to hit the trail for Romney

7/13/12 11:11 AM EDT

Months after Rick Santorum issued his low-key endorsement of Mitt Romney, ABC reports that the former White House hopeful is campaigning for Romney in his home state of Pennsylvania:

This weekend former Pennsylvania Sen. Rick Santorum will hold his first formal campaign event for Mitt Romney since he became the presumptive Republican nominee, sources close to Santorum tell ABC News.

Santorum, who emerged as one of Romney’s last opponents standing after a hard-fought primary season, will appear on Saturday at the opening of the Romney campaign’s Greensburg, Pennsylvania victory office. It’s familiar turf for Santorum who used to represent that area of southwestern Pennsylvania in Congress. ...

...Santorum was asked to participate in the Greensburg office opening by the Romney campaign and Republican party officials, and “he was happy to accept the request,” according to a source familiar with the planning of the event.

It's a significant step forward for the detente between Romney and Santorum, and a sign that the Romney campaign is willing to use Santorum's political skills and blue-collar appeal in a state and an area he's familiar with. Still, comments like this, from Iowa yesterday, show that Santorum still isn't exactly Romney's most ardent supporter, which makes his trail appearance for Romney that much more significant.